08 4.7 Gr Cherokee P0300 - JeepForum.com
 
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post #1 of 6 Old 03-12-2019, 07:21 AM Thread Starter
Megalodon47
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08 4.7 Gr Cherokee P0300

I have an 08 Gr Cherokee with a 4.7, with about 78k miles on it. Both sets of plugs (upper and lower) were changed with same brand and part number that was in it before.
About 100 miles later, car began to miss, check engine light flashing. Code P0300 was a pending code.
Over the course of the last week I have:
Put original plugs back in
Swapped coils
Swapped boots
Swapped wires
Swapped injectors
Compression tested all 8 and they are all almost identical
When at idle, at first start up, I can watch cylinders #1 and #3 misfire, then stop misfiring when idle evens out. If gas pedal depressed/engine revved, misfires come back. They also come back under load
I have just removed the intake manifold to check gasket and to see better into the cylinder.
Going to put new gasket in, but I'm at a loss at what to do next

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post #2 of 6 Old 03-12-2019, 07:54 AM
jtec
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confirm 4.7L eighth character of vin.
do you have a scanner to observe live data?

how did old plugs look - wet, dry, black, tan, steam cleaned, damaged,

FYI a flashing CEL is an attention getter as cat damage is likely if not addressed.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 6 Old 03-22-2019, 07:36 AM Thread Starter
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Quote:
Originally Posted by jtec View Post
confirm 4.7L eighth character of vin.
do you have a scanner to observe live data?

how did old plugs look - wet, dry, black, tan, steam cleaned, damaged,

FYI a flashing CEL is an attention getter as cat damage is likely if not addressed.
Yes, 4.7

I am able to monitor live data, which is how I'm able to see #1 & #3 misfiring at high cold idle then no longer misfiring at normal idle.

Old "intake" plugs dry as well as "exhaust" plugs all look identical. I'll try to see if I can post the photos of them here

Jeep has not been driven due to this issue.
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post #4 of 6 Old 03-22-2019, 08:18 AM
jtec
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Ok the term I wanted to check was GEN II engine. Making sure not confused with 5.7.

Intake and exhaust AKA upper and lower.

Are you SURE double check plugs against jeep NOT referencing what plugs you took out. Ignore this if you are original owner.


I would suggest a bottle of 'seafoam' or 'techron' some detergent for those injectors.

With scanner look at ECT, Fuel trims and B1S1 o2 sensor.
Try the old school carb trick for intake vacuum leak.

GTG back soon -

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 6 Old 03-22-2019, 10:06 PM Thread Starter
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Here's first screen of freeze frame.

If you mean spray it to find vacuum leaks, I did that before breaking out the smoke machine. I may have to post these screen shots in more than one post. I apologize for my newbness
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post #6 of 6 Old 03-22-2019, 10:08 PM Thread Starter
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next screen
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